1. Field of the Invention
The present invention relates to a transfer-type laminate film applicable to a sublimation-type thermal transfer recording system, in which an image is printed on a printing article via a thermal head and a transparent, image-protecting resin film (this is the thermal transfer laminate layer of the laminate film) is transferred under heat onto the printed surface of the article from the laminate film, and also to a thermal transfer ink sheet combined with the transfer-type laminate film.
2. Description of the Related Art
The recent tendency in the art is toward a sublimation-type thermal transfer recording system that enables expression of images with continuous full-color gradation, as the technique for hard copies of image signals.
In the sublimation-type thermal transfer recording system, a transparent film for image protection is laminated over the image as formed on printing paper for the purpose of, for example, protecting the image surface, preventing the image from being discolored or faded, and making the image surface resistant to sebum. One example of the laminate film to be used for those purposes is a transfer-type laminate film for image protection, which comprises a substrate and a thermal transfer laminate layer of a thermoplastic resin formed on the substrate.
A method for laminating such a transfer-type laminate film for image protection over images comprises placing the laminate layer of the film on the image formed on printing paper, and heating it under pressure in accordance with the image information, whereby the part of the laminate layer having been heated under pressure is transferred onto the printing paper. Using the transfer-type laminate film of that type makes the printed images have good resistance to hand-stained sebum and good resistance to plasticizers that may be in polyvinyl chloride products such as wallpaper, floor mats, tablecloths, etc.
Known is a thermal transfer ink sheet which comprises an ink layer containing a subliming dye for image formation and formed on a substrate. A technique of incorporating a transfer-type laminate film into the thermal transfer ink sheet of that type has been proposed, in which an additional thermal transfer laminate layer is formed on the substrate of the thermal transfer ink sheet, apart from the ink layer formed thereon. According to that technique, it is easy to continuously transfer the thermal transfer laminate layer onto the printed images in the printer using the ink sheet, and, in addition, the surface of the printed images is not directly contacted with sebum and plasticizers. Therefore, the technique enables ideal image protection.
The dye images formed on printing paper are discolored and faded by the action of ultraviolet rays in natural light or fluorescent lamps, etc., and are therefore problematic in that their resistance to light is not good. To solve this problem, tried is adding an ultraviolet absorbent that is solid at ordinary temperature to the thermal transfer laminate layer for the purpose of preventing ultraviolet rays causing the problem from reaching the dye images to thereby increase the resistance of the images to light.
However, adding an ultraviolet absorbent that is solid at ordinary temperature to the thermal transfer laminate layer is problematic in that, after the laminate layer containing the ultraviolet absorbent is transferred onto images, the ultraviolet absorbent gradually crystallizes and precipitates in the image surface to thereby significantly degrade the quality of the images. This problem is especially remarkable when the thermal transfer laminate layer contains a relatively large amount of such an ultraviolet absorbent.